The invention relates generally to Internet Protocol (IP) telephony and, in particular, to measurements of voice grade of service (GOS) for voice over IP (VoIP) in IP networks.
The technology for providing public and private voice service via the Internet is rapidly maturing. At present, this technology comprises IP voice gateways and/or IP telephony enabled terminals connected over legacy IP networks. Quality of service (QOS) enabled IP networks for real-time services are expected to be deployed in the near future. This advance in IP technology will effectively result in opening the telephony markets to Internet service providers (ISPs), and the like. Consequently, regulatory agencies will undoubtedly require that Service Level Agreements (SLAs) with customers be proven.
At the present time, the telecom industry uses In-service Non-intrusive Measuring Devices (INMD or NIM) for proving SLAs and for pro-active maintenance of their voice networks, both access and transmission facilities. ANSI standard T.221, Operations, Administration, Maintenance and Provisioning (OAMP) In-service Non-intrusive Measurement Device (INMD) voice service measurements are used in connection oriented TDM networks for this purpose. The ANSI standard specifies interface, measurement range and accuracy requirements for measuring voice-grade transmission parameters. The standard also describes optional functions associated with these parameters, and measurement algorithms that have been verified to meet the accuracy requirements of the standard for the measurement of speech level noise, echo path delay and information loss. Apparatus that embody this standard are commonly identified as INMD devices. The use of INMD measurement results for predicting customer opinion performance (%GOB), which is also called grade of service (GOS), is specified in a document of Alliance Telecommunications Industry Solutions (ATIS), which is a draft proposed standard T1 LB 566 xe2x80x9cin-service non-intrusive measurement device (INMD) methodology for applying INMD parameters to grade of service modelsxe2x80x9d.
In order to compete with incumbent long distance telephone carriers for market share, VOIP providers will require some mechanism to prove voice quality and network performance. There therefore exists a need for a method and apparatus for measuring voice grade of service in an IP network. No such apparatus is currently known to be available, however, and known INMD devices cannot be used to measure VOIP quality for several reasons. First, the surveillance interface points specified by the INMD standards are particular and hence restricted to connection oriented time division multiplexed (TDM) networks. It is desirable to exploit the connectionless nature of an IP telephony network to provide flexibility in locating the surveillance apparatus. Second, the need for the method and apparatus for measuring voice grade of service in an IP network also arises from the difference in performance and parameters between connection and connectionless networks. In that regard, the required method should include measuring and correlating of IP network performance parameters such as packet loss, delay and delay variation to voice grade performance and result in a set of parameters that are both measurable and meaningful for both an end user and a service provider.
At the present time, there are no IP telephony standards regarding apparatus and network performance. Until the IP telephony industry matures to require apparatus and network performance guidelines and standards, the performance of IP telephony will be highly dependent upon the implementation of voice gateways and IP network performance. Therefore, meaningful and accurate measurement of voice GOS must take into account the performance impact of the IP telephony apparatus and the IP network. In this regard, there exists a need for a method of calibrating an IP telephony apparatus and carrier network to an initial xe2x80x9cgood statexe2x80x9d, before it is commissioned for telephone service offering.
An object of the invention is to provide a non-intrusive measuring method and apparatus to assess an end-to-end IP telephony network transmission quality.
Another object of the invention is to provide a method and apparatus which make use of an In-service Non-intrusive Measurement Device (INMD) adapted for a connection oriented Time Division Multiplexer (TDM) in an IP telephony network for measurement of IP telephony transmission quality.
Yet another object of the invention is provide a method and apparatus for measuring a voice Grade of Service (GOS) and relating IP telephony network performance to the voice GOS to prove a Service Level Agreement (SLA), and for use in network maintenance.
A further object of the invention is to provide a method for calibration of the apparatus and measurement algorithms associated therewith.
In accordance with one aspect of the invention, a method for using In-service Non-intrusive Measuring Devices (INMD) for assessment of transmission quality in Internet Protocol (IP) telephony networks comprising steps:
1) collecting a group of IP datagrams of a speech sample of an end-to-end IP telephony connection from at least one IP interface point by identifying a packet flow associated with an IP telephony session;
2) processing the IP datagrams and converting the same into a format suitable for INMD process;
3) using the INMD process to assess a plurality of voice grade performance parameters related to the telephony session.
Preferably, the assessment of the voice grade performance includes computing a voice Grade Of Service (GOS) performance using a method specified in ATSI T1 LB 566.
The method preferably further comprises a step:
4) calculating a percent Good or Better (%GOB) score relevant to the voice GOS performance.
The method may further comprise a step of:
5) correlating the voice GOS performance to the IP network performance.
Preferably, the method in step 1 further comprises using header information in the IP datagrams to smooth out any delay variation in the speech sample and computing a group of network performance parameters based on the IP datagram header information.
In a preferred embodiment, step 2 further comprises determining a speech compression algorithm used in the IP datagrams by examining data encapsulated in the packets. The IP datagrams of the speech sample may be collected respectively at a far end IP interface point and a near end IP interface point.
In accordance with another aspect of the invention, an apparatus for assessment of IP telephony networks transmission quality comprises:
an In-service Non-intrusive Measurement Device (INMD) adapted to assess voice grade performance parameters in a connection oriented Time Division Multiplexer (TDM);
a processor adapted to convert a group of IP datagrams associated with an end-to-end IP telephony connection to a data format suitable for input to the INMD; and
a connection to the INMD for transferring the IP datagrams to the INMD for assessment of the voice grade performance parameters.
The apparatus preferably further comprises a data collector to collect the IP datagrams by identifying a packet flow associated with an IP telephony session.
The INMD preferably includes a function of computing a voice Grade Of Service (GOS) performance specified in ATSI T1 LB 566. Preferably, the apparatus may be selectively co-located with a Personal Computer (PC) based IP voice gateway or stand-alone in the end-to-end IP telephony connection. Also the apparatus preferably comprises a processor to correlate the voice GOS performance to IP network performance. The processor preferably comprises a Digital Signal Processor (DSP) to facilitate the computation.
In accordance with a third aspect of the invention, an initial calibration process for calibrating an IP telephony measurement apparatus comprising the steps of:
1) creating an IP datagram calibration file using speech samples having a known GOS;
2) processing IP datagrams from the IP datagram calibration file using the IP telephony measurement apparatus to convert the IP datagrams into data in a format suitable for INMD processing;
processing the data using INMD functionality of the IP telephony measurement apparatus to determine a GOS value associated with the IP datagrams;
comparing the GOS value with a GOS associated with the speech samples used to create the IP datagram calibration file; and
adjusting the IP telephony measurement apparatus until the GOS values are equal, within a certain predefined limit.
Preferably, the calibration IP datagrams are created from an IP telephony terminal during a calibration operation with a speech sample of known GOS and the output is a resultant GOS value. The comparison therefore may be conducted between the resultant GOS value and the known GOS of the speech sample.
This invention permits the IP telephony industry to measure a quality of the service they offer to their clients. Such a capability will provide not only a measure of voice GOS, but also a method of relating IP network performance to voice SLAs, which provides Internet Service Providers (ISPs) and Internet backbone network providers with guidelines for relating voice performance to network parameters that are both measurable and meaningful.
The invention exploits the connectionless nature of an IP telephony network in that the apparatus can be co-located in a voice gateway or deployed as a stand-alone apparatus, remote from a central location. The stand-alone apparatus would be required in an all-IP network scenario. Additionally, the invention takes advantages of the fact that most of the processes of the invention are already provided by voice gateways and any additional processes can be provided through software.